The present invention relates to a frequency synthesizer, and more particularly to an all-digital frequency synthesizer capable of performing a high-reliability operation.
With the development of modern multimedia entertainment systems, lots of efforts have been placed to meet the increasing demands on the resolution, bandwidth, and switching speed of frequency synthesizers. Traditionally, these requirements are achieved with the aid of the classical analog phase-locked loop (APLL) frequency synthesizer. However, the switching speed and resolution of synthesizers are becoming critically important, and conventional APLLs are not suitable to these applications because they suffer an inability to simultaneously provide fast frequency switching and high resolution without substantial design complexity. Furthermore, it is desirable to process signals all digitally to enhance noise immunity because of the relative parametric stability of digital circuits with aging and temperature variations. In addition, all-digital systems can be furnished by low supply voltage such as a voltage of 1.2V. Moreover, an all-digital circuit can be implemented with a resistor-transistor logic (RTL) based design having a feature of high productivity.